The invention relates to a process and apparatus for the parallel conveyance of a composite strand with equal speed and tension in the individual strands, wherein each individual strand is conducted between its own delivery means and a draw-off means in common to all the strands and wherein speeds and tensions in the individual strands and in the composite strand are measured, compared and controlled.
The parallel conveyance of individual strands into a composite strand with equal speed and tension in the individual single strands is required for various industrial operations. In the synthetic fiber industry, for example, individually spun filaments, threads, or small bands are conveyed by godets, piled into a composite strand and wound. In the weaving and the knitting industries, various warp beams are manufactured from a plurality of individual strands as threads, yarns, filaments or the like. Also, filaments or threads conducted in parallel are often stretched by so-called warp-stretching or band-stretching devices. Other examples may be cited in the manufacture, processing and improving of metal wires in drawing machines, in heat-treatment processes or in the twisting or cabling of individual strands into a composite strand. Still another area of thread winding technology is that in which glass fiber rovings saturated with a hardenable or curable synthetic resin are wound according to a definite widing program onto a removable or collapsible core or liner so that high quality apparatus in the form of tubes can be produced with a low weight and very favorable strength properties.
In all these processes, it is important that the individual strands of the composite strand be conveyed, treated and/or wound with equal tension and with equal speed. Otherwise, sections in the composite strand may be produced in which only individual strands are tensioned while the rest lie loose and can even form loops. If such a composite strand is to transmit tensions or pulling forces, then only the tensioned or taut strands of the individual section can do this and, insofar as their elasticity permits, these taut strands are stretched until the rest of the individual strands are likewise pulled taut and can begin to take up the tensioning forces. With further stress, however, the breaking load is reached earlier for certain single strands of the composite strand. In such a composite strand, the total load capacity is thus considerably reduced unless all the individual strands are conveyed and combined with equal tension on each single strand.
Processes for compensating briefly occurring differences of tension in the parallel delivery or conveyance of strands, especially in the winding of threads onto a common, speed-controllable winding shaft, have been proposed according to various known embodiments, for example, as disclosed in U.S. Pat. Nos. 3,350,022 and 3,672,589 and also in the German published application (DE-AS) No. 2,247,474. The purpose of these known processes is always to compensate tension differences arising between the delivered individual strands, in their production or in a preceding treatment, for example, as caused by slightly varying working conditions in the spinning of filaments or in an after-treatment zone. These prior processes also control the common winding shaft over tension rolls, dancer arms or the like acting on each individual strand, in such a way that the differences in tension are compensated. By this process, the speed control of the winding shaft takes place either over a maximal or minimal thread tension on one of the yarns or also over a difference-limiting value between established tensions in the individual strands. It has been found to be disadvantageous in the known processes to control the speed in the composite strand because only one of the strands is used, namely the one which exceeds the prescribed tension difference-limiting value which then acts on the drive motor of the common winding shaft. As a result, the tension prevailing in each of the remaining individual strands is totally disregarded.
In the other processes wherein the drive motor of the common winding shaft is controlled by a maximally or minimally permissible tension on one of the parallel conveyed individual strands, a disadvantage arises because either a retardation or an inadmissible increase in the tension on one of the individual strands is not detected, and the control of the drive motor of the common winding shaft fails to respond. Both situations, i.e. either too much or too little tension, lead to operating disturbances and are associated either with strand breakage or the undesirable formation of so-called "winders" of individual strands at the delivery means. This is especially critical where the strand material presents only a slight capacity for compensating tension differences, i.e. for example, in the case of a fully drawn wire or an unannealed, brittle and poorly extensible strand material with a high modulus of elasticity, as well as in the case of relatively large variations in strand diameter caused by the processing conditions of the conveyed individual strands. In the case of wire strands with a diameter at the upper tolerance limit, e.g. due to wear of the drawing dies, an excess delivery or overfeed preferably takes place to avoid frequent breakage of individual strands. However, such an overfeed is not well controlled within precise limits.